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import current from '/version.js'; import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem'; import CodeBlock from '@theme/CodeBlock';

Browser vendors and other organizations have built "JavaScript engines". They are independent software libraries that are capable of running JS scripts.

The most popular JavaScript engine is V8. Designed for embedding in software, it powers Chrome, NodeJS, UXP, Deno and many other platforms.

There are many other JS engines with different design goals. Some are designed for low-power or low-memory environments. Others aim for interoperability with specific programming languages or environments. Typically they support ES3 and are capable of running SheetJS code.

This demo showcases a number of JS engines and language bindings.

General Caveats

Common browser and NodeJS APIs are often missing from light-weight JS engines.

Global

Some engines do not provide globalThis or global or window. A global variable can be exposed in one line that should be run in the JS engine:

var global = (function(){ return this; }).call(null);

Console

Some engines do not provide a console object. console.log can be shimmed using the engine functionality. For example, hermes1 provides print():

var console = { log: function(x) { print(x); } };

Binary Data

Some engines do not provide easy ways to exchange binary data. For example, it is common to pass null-terminated arrays, which would truncate XLSX, XLS, and other exports. APIs that accept pointers without length should be avoided.

Base64 strings are safe for passing between JS and native code, but they should only be used when there is no safe way to pass ArrayBuffer or Uint8Array.

Byte Conventions

Java has no native concept of unsigned bytes. Values in a byte[] are clamped to the range -128 .. 127. They need to be fixed within the JS engine.

Some engines support typed arrays. The Uint8Array constructor will fix values:

var signed_data = [-48, -49, 17, -32, /* ... */]; // 0xD0 0xCF 0x11 0xE0 ...
var fixed_data = new Uint8Array(signed_data);

When Uint8Array is not supported, values can be fixed with bitwise operations:

var signed_data = [-48, -49, 17, -32, /* ... */]; // 0xD0 0xCF 0x11 0xE0 ...
var fixed_data = new Array(signed_data.length);
for(var i = 0; i < signed_data.length; ++i) fixed_data[i] = signed_data[i] & 0xFF;

Engines

This list is sorted in alphabetical order.

Boa

Boa is an embeddable JS engine written in Rust.

This demo has been moved to a dedicated page.

ChakraCore

ChakraCore is an embeddable JS engine written in C++.

This demo has been moved to a dedicated page.

Duktape

Duktape is an embeddable JS engine written in C. It has been ported to a number of exotic architectures and operating systems.

This demo has been moved to a dedicated page. The demo includes examples in C and Perl.

Goja

Goja is a pure Go implementation of ECMAScript 5.

This demo has been moved to a dedicated page.

Hermes

Hermes is an embeddable JS engine written in C++.

This demo has been moved to a dedicated page.

JavaScriptCore

iOS and MacOS ship with the JavaScriptCore framework for running JS code from Swift and Objective-C.

This demo has been moved to a dedicated page.

JerryScript

JerryScript is a lightweight JavaScript engine designed for use in low-memory environments like microcontrollers. As part of the build suite, the project generates a C library and a standalone CLI tool.

The simplest way to interact with the engine is to pass Base64 strings.

:::note pass

This demo was tested in the following deployments:

Architecture Commit Date
darwin-x64 a588e49 2023-09-22
linux-x64 a588e49 2023-09-22

:::note pass

While applications should link against the official libraries, the standalone tool is useful for verifying functionality.

:::

:::caution pass

This demo requires a much larger heap size than is normally used in JerryScript deployments! In local testing, the following sizes were needed:

This works on a Raspberry Pi.

:::

Complete Example (click to show)

Due to limitations of the standalone binary, this demo will encode a test file as a Base64 string and directly add it to an amalgamated script.

  1. Build the library and command line tool with required options:
git clone --depth=1 https://github.com/jerryscript-project/jerryscript.git
cd jerryscript
python tools/build.py --error-messages=ON --logging=ON --mem-heap=8192 --cpointer-32bit=ON
  1. Download the SheetJS Standalone script, shim script and test file. Move all three files to the jerryscript cloned repo directory:

{\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://sheetjs.com/pres.xlsx}

  1. Bundle the test file and create payload.js:
node -e "fs.writeFileSync('payload.js', 'var payload = \"' + fs.readFileSync('pres.xlsx').toString('base64') + '\";')"
  1. Create support scripts:
  • global.js creates a global variable and defines a fake console:
var global = (function(){ return this; }).call(null);
var console = { log: function(x) { print(x); } };
  • jerry.js will call XLSX.read and XLSX.utils.sheet_to_csv:
/* sheetjs (C) 2013-present  SheetJS -- https://sheetjs.com */
var wb = XLSX.read(payload, {type:'base64'});
console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]));
  1. Create the amalgamation xlsx.jerry.js:
cat global.js xlsx.full.min.js payload.js jerry.js > xlsx.jerry.js

The final script defines global before loading the standalone library. Once ready, it will read the bundled test data and print the contents as CSV.

  1. Run the script using the jerry standalone binary:
build/bin/jerry xlsx.jerry.js; echo $?

Jint

Jint is an embeddable JS engine for .NET written in C#.

This demo has been moved to a dedicated page.

Nashorn

Nashorn shipped with some versions of Java. It is now a standalone library.

This demo has been moved to a dedicated page.

QuickJS

QuickJS is an embeddable JS engine written in C. It provides a separate set of functions for interacting with the filesystem and the global object. It can run the standalone browser scripts.

This demo has been moved to a dedicated page.

Rhino

Rhino is an ES3+ engine in Java.

This demo has been moved to a dedicated page.

V8

V8 is an embeddable JS engine written in C++. It powers Chromium and Chrome, NodeJS and Deno, Adobe UXP and other platforms.

This demo has been moved to a dedicated page. The demo includes examples in C++ and Rust.

The "Python + Pandas" demo uses V8 with Python.

  1. See "Initialize Hermes" in the Hermes demo. ↩︎